• Smart Structures and Systems
• /
• v.15 no.6
• /
• pp.1439-1461
• /
• 2015

Design criteria, modeling rules, and analysis principles of seismic isolation systems have already found place in important building codes and standards such as the Uniform Building Code and ASCE/SEI 7-05. Although real behaviors of isolation systems composed of high damping or lead rubber bearings are nonlinear, equivalent linear models can be obtained using effective stiffness and damping which makes use of linear seismic analysis methods for seismic-isolated buildings possible. However, equivalent linear modeling and analysis may lead to errors in seismic response terms of multi-story buildings and thus need to be assessed comprehensively. This study investigates the accuracy of equivalent linear modeling via numerical experiments conducted on generic five-story three dimensional seismic-isolated buildings. A wide range of nonlinear isolation systems with different characteristics and their equivalent linear counterparts are subjected to historical earthquakes and isolation system displacements, top floor accelerations, story drifts, base shears, and torsional base moments are compared. Relations between the accuracy of the estimates of peak structural responses from equivalent linear models and typical characteristics of nonlinear isolation systems including effective period, rigid-body mode period, effective viscous damping ratio, and post-yield to pre-yield stiffness ratio are established. Influence of biaxial interaction and plan eccentricity are also examined.

• Smart Structures and Systems
• /
• v.15 no.5
• /
• pp.1329-1344
• /
• 2015

The stiffness of a structure is one of several structural signals that are useful indicators of the amount of damage that has been done to the structure. To accurately estimate the stiffness, an equation of motion containing a stiffness parameter must first be established by expansion as a linear series model, a Taylor series model, or a power series model. The model is then used in multivariate autoregressive modeling to estimate the structural stiffness and compare it to the theoretical value. Stiffness assessment for modeling purposes typically involves the use of one of three statistical model refinement approaches, one of which is the efficient Akaike information criterion (AIC) proposed in this paper. If a newly added component of the model results in a decrease in the AIC value, compared to the value obtained with the previously added component(s), it is statistically justifiable to retain this new component; otherwise, it should be removed. This model refinement process is repeated until all of the components of the model are shown to be statistically justifiable. In this study, this model refinement approach was compared with the two other commonly used refinement approaches: principal component analysis (PCA) and principal component regression (PCR) combined with the AIC. The results indicate that the proposed AIC approach produces more accurate structural stiffness estimates than the other two approaches.

• Structural Engineering and Mechanics
• /
• v.70 no.4
• /
• pp.421-429
• /
• 2019

This paper presents an analytical model for the estimation of initial lateral stiffness of steel moment resisting frames with masonry infills. However, rather than focusing on the single bay-single storey substructure, the developed model attempts to estimate the global stiffness of multi-storey and multi-bay frames, using an assembly of equivalent springs and taking into account the shape of the lateral loading pattern. The contribution from each infilled frame panel is included as an individual spring, whose properties are determined on the basis of established diagonal strut macro-modeling approaches from the literature. The proposed model is evaluated parametrically against numerical results from frame analyses, with varying number of frame stories, infill openings, masonry thickness and modulus of elasticity. The performance of the model is evaluated and found quite satisfactory.

• Wind and Structures
• /
• v.31 no.6
• /
• pp.561-573
• /
• 2020

Unsteady self-excited forces are commonly represented by parametric models such as rational functions. However, this requires complex multiparametric nonlinear fitting, which can be a challenging task that requires know-how. This paper explores the alternative nonparametric modeling of unsteady self-excited forces based on relations between flutter derivatives. By exploiting the properties of the transfer function of linear causal systems, we show that damping and stiffness aerodynamic derivatives are related by the Hilbert transform. This property is utilized to develop exact simplified expressions, where it is only necessary to consider the frequency dependency of either the aeroelastic damping or stiffness terms but not both simultaneously. This approach is useful if the experimental data on aerodynamic derivatives that are related to the damping are deemed more accurate than the data that are related to the stiffness or vice versa. The proposed numerical models are evaluated with numerical examples and with data from wind tunnel experiments. The presented method can evaluate any continuous fitted table of interpolation functions of various types, which are independently fitted to aeroelastic damping and stiffness terms. The results demonstrate that the proposed methodology performs well. The relations between the flutter derivatives can be used to enhance the understanding of experimental modeling of aerodynamic self-excited forces for bridge decks.

• Journal of the Korean Society for Precision Engineering
• /
• v.29 no.10
• /
• pp.1043-1049
• /
• 2012

The FEM analysis of machine tools is the general analysis process to evaluate machine performance in the industry for a long time. Despite advances in FEM software, because of difficult simplicity of CAD drawing, little experience of joints stiffness modeling and troublesome manual contact area divide for bindings, the industry designers think the FEM analysis is still an area of FEM analysis expert. In this paper, the automation of modeling process with simplicity of drawing, modeling of joints and contact area divide is aimed at easy FEM analysis to enlarge utilization of a virtual machine tools. In order to verify the effects of modeling automation, a slant bed type model with tilting table is analyzed. The results show FEM modeling automation method only needed 45 minutes to complete the whole modeling process, while manual modeling method requires almost one month with 8200 calculations for coordinate transformations and stiffness data input.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.29 no.8 s.239
• /
• pp.1153-1160
• /
• 2005

Many methods of spot weld modeling have been developed to increase efficiency and guarantee the robustness fer the CAE analysis. In this research they are introduced and the performance is compared in a viewpoint of stiffness and durability. For evaluating the performance a multi-spot welded specimen as well as two single welded specimen is used. The results show that the CWELD element considering 'patch to patch' is stiffer than other modeling methods in stiffness and more conservative in durability. It also offers simple modeling and since it is much easier to maintain the orrhogonality of the BAR element expressing a nugget, we can obtain more exact reaction forces and moments in a nugget. Therefore the CWELD element is the most excellent in the assessment of durability.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.16 no.2 s.107
• /
• pp.176-182
• /
• 2006

Modeling and verification for stability analysis of axially oscillating cantilever beams are investigated in this paper Equations of motion for the axially oscillating beams are derived and transformed into dimensionless forms. The equations include harmonically oscillating parameters which are related to the motion-induced stiffness variation. stability diagram is obtained by using the multiple scale perturbation method. To verify the accuracy of the modeling method, several points in the plane of the stability diagram are presented and solved. The present modeling method proves to be as accurate as a nonlinear finite element modeling method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.11a
• /
• pp.708-713
• /
• 2005

Modeling and verification for stability analysis of axially oscillating cantilever beams are investigated in this paper. Equations of motion for the axially oscillating beams are derived and transformed into dimensionless forms. The equations include harmonically oscillating parameters which are related to the motion-induced stiffness variation. Stability diagram is obtained by using the multiple scale perturbation method. To verify the accuracy of the modeling method, several points in the plane of the stability diagram are presented and solved. The present modeling method proves to be as accurate as a nonlinear finite element modeling method.

• Tribology and Lubricants
• /
• v.34 no.1
• /
• pp.23-32
• /
• 2018

Coupling is a mechanical component that transmits rotational force by connecting two shafts. Curvic coupling is widely used in high-performance systems because of its excellent power transmission efficiency and easy machining. However, coupling applications change dynamic behavior by reducing the stiffness of an entire system. Contact surface stiffness is an important parameter that determines the dynamic behavior of a system. In addition, the roughness profile of a contact surface is the most important parameter for obtaining contact stiffness. In this study, we theoretically establish the process of contact and bending stiffness analysis by considering the rough surface contact at Curvic coupling. Surface roughness parameters are obtained from Nayak's random process, and the normal contact stiffness of a contact surface is calculated using the Greenwood and Williamson model in the elastic region and the Jackson and Green model in the elastic-plastic region. The shape of the Curvic coupling contact surface is obtained by modeling a machined shape through an actual machining tool. Based on this modeling, we find the maximum number of gear teeth that can be machined according to the contact angle. Curvic coupling stiffness is calculated by considering the contact angle, and the calculation process is divided into stick and slip conditions. Based on this process, we investigate the stiffness characteristics according to the contact angle.

• Journal of KSNVE
• /
• v.9 no.5
• /
• pp.975-983
• /
• 1999

This paper describes the dynamic characteristics of the joint structures in case of using the simplified beam model in the F. E. analysis. The modeling errors, when replace the shell with the beam, are investigated through F. E. normal modes analysis. Normal mode analysis were performed to obtain the natural frequencies of the L and T shaped joints with various type of channels. The results were analyzed to access the effects of the models on the accuracy of F.E. analysis by identifying the geometric factors which cause the error. The geometric factors considered are joint angle, channel length, thickness and area ratio of the hollow section to the filled one. The joint stiffness evaluation technique is developed in this study using normal modes analysis with Lumped Mass. With this method, the progressively improved results of F. E. analysis are obtained using the simplified beam model. The static and normal modes analysis are performed with the joint stiffness values obtained by the Kazunori Shimonkakis' virtual stiffness method and the proposed method and these simplified modeling errors are compared.